Biomarker analysis of phase II pembrolizumab maintenance treatment after chemotherapy response in patients with HER2-negative inflammatory breast cancer and triple-negative breast cancer.
Authors: Toshiaki Iwase, Angela Alexander, Evan N. Cohen, Hui Gao, Vivian Y Chiv, Megumi Kai, Kumiko Kida, Savitri Krishnamurthy, Dianne Liu, Yu Shen, David Luis Ramirez, Alexandre Reuben, Debu Tripathy, Daniel J. Booser, Stacy L. Moulder, Clinton Yam, Vicente Valero, Bora Lim, James M. Reuben, Naoto T. Ueno
Journal: Journal of Clinical Oncology (2023)

1105 Background: Accumulating toxicities make indefinite chemotherapy unfeasible for many patients with metastatic/recurrent HER2-negative inflammatory breast cancer (IBC) or triple-negative breast cancer (TNBC). We conducted a single-arm phase II trial of pembrolizumab monotherapy to determine the efficacy of maintenance immunotherapy in patients with metastatic HER2-negative aggressive breast cancer and to identify biomarkers correlated with disease control. Methods: The study enrolled patients who had a complete response, partial response, or stable disease after a minimum of 3 cycles of chemotherapy for metastatic TNBC/IBC regardless of PD-L1 expression between 2015 and 2022. Pembrolizumab was administered at 200 mg every 3 weeks until disease progression, intolerable toxicity, or 2 years of exposure to the drug. The primary endpoint was the 4-month disease control rate (DCR), and the secondary endpoint was progression-free survival (PFS). Correlative studies were performed to determine associations between clinical response, and immune profiling consisting of T-cell clonality, immunophenotyping, and dendritic cell (DC) function with blood collected at baseline and after 2 cycles of pembrolizumab treatment. Results: Of 43 treated patients, 11 had metastatic IBC and 32 had TNBC. The median number of prior lines of chemotherapy for metastatic disease was 1. During a median follow-up of 11.4 months, 33 patients had progressive disease and 25 were deceased. The 4-month DCR was 58.1% (95% CI: 43.4%-72.9%) and the median PFS was 4.8 months (95% CI: 3.0-7.1 months). The median PFS of the metastatic IBC group (2.2 months) and TNBC group (4.8 months) did not differ significantly ( p = .12). Thirty-one patients discontinued treatment due to progressive disease rather than toxicity. Observed toxicities were consistent with the known profile of pembrolizumab. Correlative blood studies showed availability of PD-1 on CD8 T cells decreased on therapy. T-cell exhaustion markers 2B4, CTLA4, and TIM3 decreased in patients who had therapeutic benefit, while LAG3 increased in patients without benefit. During therapy, ex vivo cytokine synthesis (IL-6/IL-12/TNFα) by DCs was superior in patients who benefited from therapy and increased from pretreatment samples. High T-cell clonality at baseline predicted response to immunotherapy (10.4 vs 3.6 months, p = .04). Additionally, patients exhibiting the greatest clinical benefit also had a significant increase in T-cell clonality over the course of therapy (20% vs 5.9% mean increase, p = .04). Conclusions: Increased T-cell clonality and DC activity, along with reductions in T-cell exhaustion, were associated with prolonged disease control following pembrolizumab maintenance therapy, achieving acceptable disease control with manageable toxicity. Clinical trial information: NCT02411656 .